The invention relates to a multilayer pearl lustre pigment having a pronounced colour flop, based on a platelet-shaped substrate comprising a material of low refractive index in the range from 1.35 to 1.8.
Multilayer pigments which exhibit an angle-dependent colour change between two or more intensive interference colours are known.
For instance, U.S. Pat. No. 4,434,010 describes a multilayer interference pigment consisting of a central layer of a reflective material (aluminium) and alternating layers of two transparent, dielectric materials of high and low refractive index, for example titanium dioxide and silicon dioxide, on either side of the central aluminium layer. In a further embodiment of the pigment, the layers following the central aluminium layer are formed by magnesium fluoride and chromium. This pigment exhibits an intensive colour flop from green to purplish red.
EP 0 753 545 describes goniochromatic lustre pigments based on transparent, non-metallic, platelet-shaped substrates, which have at least one layer stack comprising a colourless coating with a refractive index nxe2x89xa61.8 and a reflective, selectively or non-selectively absorbing coating which is at least partly transparent to visible light, and which also have, if desired, an external protective layer in addition.
These pigments have the disadvantage that they are produced by a technically very complex and costly process, for example by chemical vapour deposition (CVD) or physical vapour deposition (PVD) techniques. Further disadvantages are the frequent difficulty in reproducing the pigments in the desired product quality, and their deficient weathering stability.